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CONNECTICUT 


Is 


Agricultural  Experiment  Station 


NEW  HAVEN,  CONN. 


BULLETIN  246 


FEBRUARY,  1923 


The  Apple  and  Thorn 
Skeletonizer 

By  B.  A.  Porter  and  Philip  Garman. 


Figure  1.     A  skeletonized  apple  leaf. 


CONTENTS. 

PAGE 


Introduction    247 

History    and    Distribution....  248 

Importance    248 

Common  Name   249 

Food  Plants  *.  .■ 249 

Synonymy   250 

Descriptions    250 

Observations  in  1922 253 


PAGE 

Habits  of  the  Moths 256 

Dissemination  of  the  Moths..  256 

Hibernation    256 

Life    History    Data 257 

Natural   Enemies 260 

Control    261 

Summary     263 

Bibliography    263 


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^y 


CONNECTICUT  AORICILTLRAL  EXPERI^IENT  STATION 

OrflCERS  AND  STAFr 
February,  1923 


BOARD  OF  CONTROL. 
His  Excellency,  Charles  A.  Templeton,  cx-officio,  President. 

James  H.  Webb,  Vice  President  Hamden 

George  A.  Hopson,  Secretary   Mt.  Carmel 

E.  H.  Jenkins,  Director  and  Treasurer  New  Haven 

Joseph  W.  Alsop Avon 

Charles  R.  Treat   Orange 

Elijah   Rogers    Southington 

Edward  C.  Schneider   Middletown 


Administration. 


Chemistry: 
Analytical  Laboratory. 


Biochemical 
Laboratory. 
Botany. 


Entomology. 


Forestry. 


Plant  Breeding. 

Tobacco  Sub-Station 
at  Windsor. 


STAFF. 

E.  II.  Jenkins,  Ph.D.,  Director  and  Treasurer. 

W.  L.  Slate,  B.Sc,   Vice  Director. 

Miss  L.  M.  Brautlecht,  Librarian  and  Bookkeeper. 

Miss  J.  V.  Berger,  Stenographer  and  Bookkeeper. 

William  Veitch,  In  cliarge  of  Buildings  and  Grounds. 

E.   Monroe  Bailey,  Ph.D.,   Cliemist  in  Charge. 

R.  E.  Andrew,  M.A.  v 

C.  E.  Shepard,  (      ,     .  ^,       • 

„  ,     ,,  >  .-issistaiit   Chemists. 

Owen  L.  Nolan,  I 

Harry  J.   Fisher,  A.B.       ) 

Frank  Sheldon,  Laboratory  Assistant. 

V.  L.  Churchill,  Sampling  Agent. 

Mrs.  B.  p.  Storrs,  Clerk. 

T.  B.  Osborne,  Ph.D.,  D.Sc,  Chemist  in  Charge'. 

G.  P.  Clinton,  Sc.D.,  Botanist  in  Cliarge. 

E.  M.  Stoddard,  B.  S.,  Pomologist. 

Miss  Florence  A.  McCormick,  Ph.D.,  Pathologist. 

G.  E.  Graham,  General  Assistant. 

Mrs.  W.  W.  Kelsey,  Secretary. 

W.   E.   Britton,   Ph.D.,   Entomologist  in   Charge;  State  Ento- 
mologist. 
B.  H.  Walden,  B.Agr.,  M.   P.   Zappe,   B.S.,  )  Assistant. 
Philip  Garman,  Ph.D.  )       Entomologists. 

John  T.  Ashworth,  Deputy  in  Charge  of  Gipsy  Moth  Work. 
Samuel  T.  Sealy,  Deputy  in  Charge  of  Mosquito  Control. 
Miss  Gladys  M.  Finley,  Stenographer. 
Walter  Q.  Filley,  Forester  in  Charge. 
A.  E.  Moss,  M.  F.,  Assistant. 
H.  W.  HicocK,  M.F.,  Assistant. 
Miss  Pauline  A.  Merchant,  Stenographer. 
Donald  F.  Jones,   S.D.,  Plant  Breeder. 
P.   C.  Mangelsdorf,  B.S.,  Assistant. 

G.  H.  Chapman,  Ph.D.,  in  Cliarge. 


The  Apple  and  Thorn  Skeletonizer 

H enter ophila  pariana  (Clerck) 


BY 


Bennet  a.  Porter*,  Entomologist,  Bureau  of  Entomology, 
United  States  Department  of  Agriculture, 


AND 


Philip   Garman,   Assistant   Entomologist,   Connecticut 
Agricultural  Experiment  Station. 


Introduction. 


In  August  and  September,  1922,  numerous  brown  and  defoliated 
apple  trees  in  Connecticut  caused  much  comment.  Later,  inquiries 
were  frequent  regarding  the  "little  triangular  black  bugs"  that 
were  common  everywhere,  especially  on  window  screens.  These 
comments  and  inquiries  were  caused  by  the  appearance  of  an  in- 
sect, the  apple  and  thorn  skeletonizer,  known  to  entomologists  as 
Hemerophila  pariana  (Clerck),  and  the  "bugs"  seen  on  screens 
were  tiny  moths,  the  adult  form,  in  which  stage  they  probably 
pass  the  winter.  Like  many  of  our  pests,  the  insect  has  found  its 
way  here  from  Europe  and,  being  unchecked  by  its  usual  enemies, 
has  multiplied  abundantly. 

In  view  of  the  importance  of  this  new  addition  to  our  list  of  in- 
sect pests,  the  writers  have  made  a  study  of  its  life  history,  and 
the  information  obtained,  although  incomplete  in  some  respects, 
is  here  presented. 

The  work  of  the  senior  author  was  carried  on  at  the  field  sta- 
tion maintained  for  the  study  of  fruit  insects  by  the  U.  S.  Bureau 
of  Entomology  at  Wallingford.  This  station  is  under  the  general 
direction  of  Dr.  A.  L.  Ouaintance  of  the  Bureau,  and  work  is  con- 


*  Note :  Dr.  Porter,  who  has  been  in  charge  of  the  U.  S.  Bureau  of 
Entomology  Field  Station  at  Wallingford,  Conn.,  has  studied  this  insect 
and  has  written  the  major  portion  of  this  paper.  Dr.  Garman  of  this  Sta- 
tion has  also  made  rearings  and  observations  on  this  insect  independently 
of  Dr.  Porter.  At  my  suggestion  they  have  put  their  notes  together  in  the 
preparation  of  this  bulletin.  [W.  E.  Britton.] 


248  CONNECTICUT  EXPERIMENT  STATION  BULLETIN   246. 

ducted  in  co-operation  with  the  Connecticut  Agricultural  Experi- 
ment Station  at  New  Haven.* 

History  and  Distribution. 

This  insect  has  been  known  to  European  entomologists  for  over 
160  years,  and  frequent  reference  is  made  to  it  in  Old  World 
entomological  literature.  The  species  occurs  throughout  western 
Europe  except  the  extreme  southern  part,  and  is  recorded  as  far 
north  as  Norway,  in  many  parts  of  eastern  and  southern  European 
Russia,  and  in  Turkestan  in  western  Asia. 

In  August,  1917,  Dr.  E.  P.  Felt  discovered  that  the  insect  was 
present  in  Westchester  County,  N.  Y.,  in  the  lower  Hudson  River 
Valley.  For  the  next  two  or  three  years  the  skeletonizer  spread 
gradually  to  the  northward  and  eastward.  In  the  fall  of  1920  it 
was  found  in  Connecticut  at  Greenwich  and  Stamford,  and  was  re- 
ported by  Dr.  Britton  in  his  Annual  Report  for  1920  and  in  the 
Proceedings  of  the  Connecticut  Pomological  Society  for  the  same 
year. 

Since  1920  the  spread  of  the  pest  seems  to  have  gained  in 
momentum,  and  in  Dr.  Britton's  1921  Report  it  was  mentioned  as 
occurring  in  all  parts  of  the  State  except  Windham  County.  The 
infested  area  now  includes  the  Hudson  River  Valley  as  far  north 
as  Albany,  practically  the  entire  State  of  Connecticut,  and  parts  of 
western  Massachusetts.  During  October  large  numbers  of  moths 
were  noted  at  Amherst,  Mass.,  and  the  insect  will  probably  be 
found  in  southern  New  Hampshire  and  Vermont  the  com- 
ing year.  The  spread  from  the  point  where  the  skeletonizer  was 
first  noted  has  been  almost  wholly  to  the  northward  and  east- 
ward, since  it  does  not  seem  to  have  extended  its  range  very  far 
into  New  Jersey. 

In  March  of  1922  the  insect  was  also  reported  in  Northern 
Japan,  where  its  life  history  is  similar  to  that  in  Connecticut. 

Importance. 

Since  its  arrival,  the  skeletonizer  has  caused  serious  damage  in 
many  parts  of  Connecticut,  especially  in  small  home  orchards  and 
in  orchards  which  were  not  carefully  sprayed.  Many  unsprayed 
trees  were  seriously  damaged  before  midsummer  last  year,  and  by 


*During  the  summer  of  1922  the  senior  author  was  ably  assisted  in  the 
life  history  studies  by  Mr.  Stanley  W.  Bromley,  then  a  Field  Assistant  in 
the  Bureau,  and  now  a  graduate  student  at  the  Massachusetts  Agricultural 
College.  Thanks  are  here  extended  to  Mr  S.  A.  Rohwer,  Mr.  R.  A.  Cushman 
and  Dr.  J.  M.  Aldrich,  of  the  Bureau  of  Entomology,  for  the  identification  of 
parasite  material  reared  from  the  skeletonizer.  Hearty  thanks  are  also 
due  Mr.  B.  H.  Walden  of  the  Station,  for  assistance  in  preparing  the  illus- 
trations for  publication. 


APPLE  AND   THORN   SKELETONIZER.  249 

late  August  all  the  leaves  on  many  of  them  were  brown  and  dry, 
faUing  early  in  September.  Plate  IV,  a,  shows  a  tree  which  was 
injured  by  an  unusually  severe  infestation.  Late  in  August  nearly 
every  leaf  on  this  tree  had  been  totally  skeletonized,  although  most 
of  the  larvae  were  not  more  than  two-thirds  grown.  With  famine 
staring  them  in  the  face,  many  of  the  caterpillars  left  their  de- 
pleted feeding  ground  in  search  of  fresh  food,  spinning  down  on 
threads  and  crawling  here  and  there.  So  many  larvae  laid  threads 
over  the  same  ground  that  the  trunk  of  the  tree  became  enclosed 
in  a  web  similar  to  a  huge  tent  caterpillar  nest.  Early  in  Septem- 
ber most  of  the  leaves  on  this  tree  were  falling,  and  by  the  middle 
of  the  month  it  was  bare.  Similar  injury  was  done  in  many  parts 
of  the  State,  especially  on  roadside  trees  and  in  smaller  orchards. 
This  injury  to  the  foliage  throughout  the  season,  which  in  extreme 
cases  means  complete  defoliation  by  September  or  even  earlier, 
weakens  the  tree,  lessens  the  amount  of  reserve  food  stored,  and 
reduces  the  vitality  of  the  blossom  buds  for  the  coming  season. 

Commercial  growers  will  have  little  to  fear  from  this  insect, 
as  the  routine  spray  applications  will  ordinarily  keep  the  pest  from 
getting  a  start  in  the  orchard.  The  future  importance  of  the 
skeletonizer  cannot  be  safely  predicted,  but  it  is  to  be  hoped  that 
before  long  it  may  be  brought  under  control  by  climatic  conditions 
or  by  its  natural  enemies,  and  will  take  its  place  among  our  native 
and  long  established  pests.  The  infestation  in  southwestern 
Connecticut  is  reported  by  one  observer  as  being  less  severe  in 
1922  than  in  1921,  which  may  be  taken  by  the  optimistic  to  indi- 
cate the  future  trend  of  the  infestation. 

Common  Name. 

In  most  American  accounts  the  pest  has  been  called  the  "apple 
and  thorn  skeletonizer".  Although  this  common  name  is  not  en- 
tirely satisfactory,  no  attempt  will  be  made  here  to  suggest  a  new 
one.  However,  throughout  this  paper  the  insect  is  referred  to 
for  the  most  part  simply  as  the  "skeletonizer". 


Food  Plants. 

In  Europe  the  skeletonizer  is  recorded  as  feeding  on  apple, 
thorn,  pear,  mountain  ash,  birch,  one  species  of  plum,  and  possibly 
willow.  Apple  seems  to  be  the  preferred  food  plant,  and  many 
accounts  speak  of  it  solely  as  an  apple  pest  and  make  no  mention 
of  other  hosts. 

In  the  United  States  it  has  been  noted  chiefly  on  apple,  to  a 
lesser  extent  on  thorn  and  pear,  and  in  one  instance  on  sweet 
cherry,  but  it  does  not  seem  to  have  been  found  on  any  of  the  other 
host  plants  listed  in  Europe. 


250  CONNECTICUT  EXPERIMENT  STATION   BULLETIN   246. 

A  similar  injury  occurred  on  gray  and  other  birches  in  New 
England  the  past  season,  which  was  attributed  by  many  persons 
to  this  insect.  The  cause  of  the  injury  to  the  birches,  however,  is 
a  native  insect,  known  as  the  "birch  leaf  skeletonizer."  {Buccula- 
trix  canadensisella  Chambers).  Outbreaks  of  this  species  have 
occurred  at  intervals  of  about  ten  years  since  1892. 


Synonymy. 

This  insect  has  been  known  to  entomologists  under  a  number 
of  scientific  names  during  the  past  century  and  a  half.  Among 
these  are  the  following: 

Phalaena   (Tortrix)   pariana  Clerck 

1759 — Icones  Insectorum,  t.  10,  f.  9. 
Pwalis  pariana  (Clerck) 

1794— Fab.,  Ent.  Syst.,  Ill  2,  p.  277,  No.  148. 
H enter ophila  pariana  (Clerck) 

1806 — Hiibner,  Tentamen. 
Anthophila  liitosa  Haworth 

1812— Lep.  Britt.,  Ill,  p.  472,  No.  4. 
Choreutis  pariana   (Clerck)  Ij 

1826 — Hiibner,  Verzeichniss  Bekannten  Schmetterlinge,  p.  373. 
Asopia  parialis  Treitsclike  ,  ; 

1829— Schmett.  Europe,  VII,  p.  159. 
Simaethis  pariana   (Clerck) 

1829— Stephens,  Catal.,  II,  p.  161,  No.  6782. 

Hemer ophila  pariana  (Clerck) 

1900— Fernald,  C.  H.,  Can.  Ent.,  32,  p.  236. 
Xylopoda  pariana  (Clerck) 

1903— Tutt,  J.  W.,  Ent.  Rec.  and  Journ.  of  Var.,  15,  p.  242. 


Descriptions. 

The  following  brief  outline  will  give  a  general  idea  of  the  ap- 
pearance of  the  insect  in  its  successive  stages. 

The  form  in  which  the  skeletonizer  does  its  damage  to  the  apple 
foliage  is  that  of  a  small  caterpillar.  When  newly  hatched  it  meas- 
ures about  one-twenty-fifth  of  an  inch  in  length,  and  is  a  pale  yel- 
lowish green.  When  full  grown  it  has  become  nearly  half  an  inch 
in  length,  and  is  yellowish  green  with  numerous  prominent  black 
spots.  After  feeding  is  completed,  a  long  narrow  white  cocoon 
about  three- fourths  of  an  inch  to  an  inch  in  length  is  constructed 
in  a  fold  of  an  apple  leaf  or  elsewhere,  and  f-rom  this  the  adult 
emerges  in  due  time.  The  moth  is  more  or  less  triangular  in  shape 
when  resting,  brown  or  dark  gray  in  color,  usually  with  a  purpHsh 
tinge.  It  has  a  very  characteristic  attitude,  the  wings  usually  being 
held  in  an  oblique  position,  slanting  upwards  from  the  fore  part 
of  the  body  at  an  angle  of  about  30°  with  the  surface  on  which  it 


APPLE   AND   THORN    SKELETONIZER.  25 1 

is    resting".     The    eggs  are    somewhat   hemispherical,  about    one- 
sixtieth  of  an  inch  in  diameter,  and  are  pale  yellowish  green,  with 
a  brownish  ring  which  usually  develops  before  hatching. 
More  detailed  descriptions  of  the  different  stages  follow : 


The  Egg— 

Sub-hemispherical  in  shape,  often  slightly  longer  than  wide ; 
measuring  as  follows :  length — .39  mm.  to  .44  mm.,  average  .41 
mm.;  width — .33  mm.  to  .44  mm.,  average  .38  mm.;  height — .19 
mm.  to  .28  mm.,  average  .23  mm.  The  partially  flattened  side  is 
usually  placed  next  the  surface  to  which  the  egg  is  applied.  It  is 
soft,  thin  shelled,  finely  sculptured,  with  fine  lines  radiating  from  a 
point  in  the  center  of  the  rounded  surface  of  the  egg.  When  first 
laid  the  eggs  are  pale  green ;  after  a  few  days  they  take  on  a 
slight  yellowish  tinge,  and  many  of  them  show  a  brownish  ring 
which  has  a  diameter  about  half  or  more  of  the  diameter  of  the 
egg,  and  which  varies  in  width,  being  sometimes  narrow,  and  some- 
times broad  enough  to  occupy  the  greater  part  of  the  convex  sur- 
face. 


The  Larva — 

First  Insfar — Length,  newly  hatched — about  .8  mm. ;  length, 
full  fed — 2.0  mm.;  width  of  head — .17  mm.  to  .22  mm.;  average, 
.18  mm.  Body  distinctly  annular.  Head,  pale  yellow  brown, 
posterior  lateral  margin  with  a  dark  line.  Thoracic  legs  and  pro- 
legs  a  translucent  pale  watery  green. 

Second  Instar- — General  color  pale  yellowish  green  with  dark 
tubercles.  Length,  full  fed — 3.5  mm. ;  width,  head — .30  mm.  to 
.33  mm. ;  average  .33  mm.  Head,  light  yellowish  brown ;  ocelli 
and  posterior  lateral  margin  dark ;  tips  of  mouth  parts,  brown. 
Tubercles  raised,  dark,  conspicuous.  Legs  and  prolegs,  pale,  trans- 
lucent. 

Third  Instar — Very  similar  to  preceding  instar,  the  dark  tuber- 
cles becoming  larger.  Length,  full  fed — 6.0  to  7.0  mm. ;  width, 
liead — .52  mm.  to  .61  mm. ;  average,  .55  mm.  Head,  light  yellow- 
ish brown ;  ocelli  and  posterior  lateral  margin  dark ;  tips  of  mouth 
parts,  brown;  upper  part  of  head  "usually  with  two  dusky  spots. 
Legs,  dusky  distally ;  prolegs,  slender,  pale,  translucent. 

Fourth  Instar  (Full  grown) — Length,  full  fed — 10  mm.  to  12 
mm. ;  width,  head — .88  mm.  to  .96  mm. ;  average,  .90  mm.  Yellow- 
ish green  with  prominent  black  tubercles.  Head,  pale  brown ; 
posterior  lateral  edge,  ocelli,  and  a  narrow  line  at  edge  of  mouth 
parts,  black;  often  a  pair  of  dusky  spots  on  upper  front  of  heaid. 
The  median  dorsal  area,  also  a  round  lateral  area  on  each  segment, 


252  CONNECTICUT  EXPERIMENT  STATION   BULLETIN   246. 

a  more  yellowish  green ;  tubercles  large,  prominent,  shining  black, 
finely  lined.  Ventral  surface  paler;  last  two  joints  of  thoracic 
legs  dusky,  the  next  to  the  last  especially  so,  rest  of  legs  about 
concolorous  with  body ;  prolegs  pale,  slender,  tubular,  with  a  com- 
plete circle  of  hooks  at  the  tip  of  all  except  the  posterior.  See 
figure  2,  a. 


Figure  2.  Apple  and  thorn  skeletonizer.  a.  larva ;  b.  female  pupa ;  c. 
caudal  extremity  of  male  pupa,  all  greatly  enlarged.  Drawing  lent  by  U.  S. 
Bureau  of  Entomology. 

The  Pupa- 
Length — 5.0  mm.  to  5.8  mm.,  average,  5.4  mm. ;  width  at 
widest  point — 1.6  mm.  to  1.9  mm. ;  average,  1.8  mm.  Blunt  at  the 
ends.  When  newly  formed  is  a  light  yellowish  brown,  with  the 
outline  of  antennae,  legs,  wing  pads,  abdominal  segments,  and 
spiracles  darker ;  eyes  reddish.  Later  the  entire  pupa  becomes 
darker,  the  head  and  abdominal  segments  9-10  becoming  nearly 
black ;  and  the  anterior  portions  of  the  meso-and  metathorax, 
legs,  and  tips  of  antennae,  more  dusky  than  the  rest  of  the  pupa. 
On  the  anterior  part  of  dorsal  abdominal  segments  3-8  in  the  male 
and  2i-7  in  the  female  is  a  single  row  of  very  fine,  short  spines, 
which  in  living  specimens  are  often  telescoped  under  the  margin 
of  each  preceding  segment.  Segment  10  has  two  short,  dorsal 
spines.  Body  with  a  few  fine  setae.  The  abdominal  segments 
beyond  the  middle  are  very  movable,  and  when  disturbed  the  pupa 
moves  the  tip  of  the  abdomen  vigorously.     See  figure  2,  b  and  c. 


The  Moth — 

The  moth  is  extremely  variable.  The  predominant  color,  how- 
ever, is  dark  reddish  brown,  often  with  a  purplish  tinge.  Mar- 
ginal scales  of  the  wings  nearly  always  d^rk  brown,  but  the  color 


APPLE  AND   THORN   SKELETONIZER.  253 

of  the  front  wings  is  often  relieved  by  an  indefinite  pale  band  (see 
Plate  II,  b  and  d),  and  wavy  black  lines.  Frequently  there  are 
three  or  four  white  spots  along  the  costal  margin  of  the  front 
wing,  but  the  whole  may  be  uniform  brown  or  gray  with  spots  or 
bands  or  stripes  indistinct.  Hind  wings  with  a  pale  stripe  on 
the  costal  margin  which  extends  from  the  base  of  the  wing  slightly 
beyond  the  middle.  The  labial  palpi  consist  of  three  segments,  of 
which  the  third  or  terminal  segment  is  three-fourths  the  length  of 
the  middle  one.  They  are  clothed  with  brown  or  white-tipped 
scales  and  extend  beyond  the  head  the  length  of  the  terminal 
segment.  The  wings  below  are  mostly  grayish  in  appearance,  the 
costal  margins  of  the  front  wings  with  conspicuous  pale  spots. 

Body  clothed  with  brown  scales  above  except  on  sides  of  the 
abdomen  where  they  are  gray-tipped.  Venter  of  abdomen  and  legs 
with  grav-tipped  scales,  the  tarsal  segments  with  white  scales  at 
tip. 

Length  of  body.  4.5  to  5  mm. ;  length  of  front  wings,  5  mm. ; 
wing-spread,  11-13  mm. 

Observations  in   1922. 

While  definite  proof  is  lacking  as  to  the  stage  in  which  the  skel- 
etonizer  passes  the  winter,  our  observations  indicate  that,  for  the 
most  part,  hibernation  occurs  in  the  adult  stage.  Moths  were 
noted  in  the  field  near  WaUingford  on  April  16th  and  April  26th, 
and  egg-laying  evidently  begins  as  early  as  the  leaves  appear,  since 
larvae  were  found  in  various  stages  during  May,  and  cocoons  were 
spun  as  early  as  May  28th.  A  second  generation  followed  soon 
after  the  first,  larvae  of  this  brood  being  present  in  the  latter  part 
of  June,  and  some  of  them  reaching  maturitv  by  the  middle  of 

July. 

OVIPOSITION. 

From  this  point,  our  life  history  studies  are  more  complete,  due 
to  the  increasing  abundance  of  the  skeletonizers,  and  to  the  fact 
that  moths  were  induced  to  lay  eggs  in  captivity,  providing  abun- 
dant material  in  all  stages.  This  was  accomplished  by  placing 
fairly  large  numbers  of  moths  (usually  forty  or  more)  in  glass 
battery  jars,  supplying  them  with  a  dilute  sugar  solution  in  tufts 
of  cotton,  and  providing  apple  foliage  on  which  to  place  the  eggs. 
On  emergence,  the  moths  are  apparently  not  ready  to  oviposit,  as 
no  eggs  were  laid  in  any  of  the  cages  until  the  fifth  day,  and  in 
one  cage  none  were  laid  until  the  tenth  day  after  the  moths  had 
left  the  cocoons.  While  a  few  are  laid  on  the  upper  surface  of  the 
leaves,  the  majority  of  the  minute,  green,  sub-hemispherical  eggs 
are  placed  on  the  lower  surface,  usually  next  the  midrib  or  a  larger 
vein,  often  being  tucked  partly  under  it.     Usually  the  flattened 


254  CONNECTICUT  EXPERIMENT  STATION  BULLETIN   246. 

side  of  the  egg  is  placed  next  the  surface  on  which  it  is  laid, 
though  occasionally  the  egg  is  placed  on  edge  among  a  mass  of  leaf 
hairs.  Ordinarily  laid  singly,  the  eggs  when  numerous  may  touch 
each  other  or  overlap  slightly.  Not  all  are  laid  at  one  time,  as 
with  some  species  of  insects,  but  they  mature  a  few  at  a  time  over 
an  extended  period.  After  the  moths  commenced  laying,  eggs 
were  deposited  daily  for  two  to  three  weeks.  In  the  five  jars  used 
for  second  brood  oviposition  the  average  number  of  eggs  recorded 
per  moth  in  each  jar  was  52,  52,  76,  80,  and  94,  respectively,  and 
no  doubt  some  additional  eggs  were  overlooked,  tiny  and  incon- 
spicuous as  they  are.  Possibly  more  eggs  are  laid  normally  in  the 
field  than  it  was  possible  to  obtain  in  captivity.  Most  of  the  moths 
lived  at  least  two  or  three  weeks,  and  most  of  them  continued 
alive  several  weeks  after  egg-laying  stopped,  the  maximum  length 
of  life  recorded  being  forty-two  days  for  a  female,  and  forty-eight 
days  for  a  male. 

INCUBATION   OF  EGGS. 

As  the  embryo  larva  develops,  the  egg  turns  from  a  pale  green 
to  a  slightly  yellowish  green,  and  a  brownish  ring  appears  in  the 
convex  surface.  As  hatching  time  approaches,  the  form  of  the 
larva  may  be  very  faintly  seen  through  the  thin  shell  of  the  egg, 
and  the  ocelli  show  as  dark  red  dots.  During  the  summer,  the 
eggs  hatch  about  a  week  after  being  laid. 

FEEDING   HABITS. 

On  hatching,  the  tiny  pale  green  larvae  wander  for  a  while  over, 
the  lower  surface  of  the  leaf,  feeding  a  little  here  and  there,  but 
soon  settle  down  in  one  spot,  sometimes  several  in  company,  and 
eat  away  small  patches  of  the  lower  leaf  surface.  Over  the  feed-' 
ing  area  is  spun  a  loosely  woven  layer  of  silk,  which  soon  becomes 
filled  with  dark  bits  of  waste  matter.  The  skeletonizer  larvae  pass 
rapidly  through  four  stages  or  ihstars,  shedding  their  skins  at  the 
close  of  each.  After  the  first  molt,  numerous  dark  dots  appear  on 
the  upper  side  of  the  body ;  these  become  more  and  more  con- 
spicuous with  each  succeeding  instar.  When  about  one-third 
grown,  usually  during  the  second  instar,  the  larvae  desert  the  orig- 
inal feeding  areas  on  the  lower  surface  of  the  leaves,  and  migrate 
to  the  upper  side.  There  a  light  web  of  silk  is  spun  across  from 
opposite  edges  of  the  leaf,  usually  near  the  base  or  the  tip,  draw- 
ing the  two  edges  of  the  leaf  partly  together.  Under  this  web  the 
larva  feeds  on  the  leaf  tissue,  consuming  all  except  the  opposite 
epidermis  and  the  veins.  Often  several  larvae  of  various  sizes 
may  be  found  under  a  single  web,  especially  when  they  are 
abundant.  In  many  cases  a  partially  skeletonized  leaf  will  be  de- 
serted   for   a    fresh    one    nearby.      When    disturbed,    the    larvae 


APPLE   AND   THORN    SKELETONIZER.  255 

wriggle  vigorously  and  drop  on  a  fine  silken  thread.  When  nearly 
full  grown,  they  often  spin  down  in  the  same  way,  especially  if 
the  food  supply  is  becoming  depleted  due  to  excessive  numbers  of 
the  voracious  caterpillars. 


THE  COCOONING  PERIOD. 

After  feeding  for  three  weeks  or  more,  the  larvae  become  full 
grown,  and  make  preparations  for  their  coming  transformation. 
The  cocoon  is  usually  constructed  in  an  angle  or  fold  of  a  leaf, 
often  along  the  midrib,  sometimes  in  the  last  leaf  fed  upon,  but 
more  often  in  another.  Besides  apple  leaves,  numerous  other 
places  may  be  used  for  cocooning,  such  as  cracks  in  buildings, 
leaves  of  various  weeds,  and  so  on.  The  cocoon  is  white, 
about  three- fourths-  of  an  inch  long  and  rather  narrow.  The 
cocoon  proper  is  enclosed  in  an  outer  one,  which  consists  of  a 
double  layer  of  silk,  stretched  between  the  opposite  sides  of  the 
fold  or  curl  of  the  leaf,  with  a  smaller  amount  of  silk  woven  next 
to  the  leaf  itself.  The  inner  cocoon  is  spindle  shaped,  pointed  at 
the  ends,  a  little  shorter  than  the  outer  cocoon  and  considerably 
narrower,  and,  like  the  outer  one,  is  composed  of  a  double  layer 
of  silk.  Both  ends  are  open,  and  the  last  larval  skin,  cast  ofif  when 
the  pupa  was  formed,  is  often  pushed  out  into  the  space  between 
the  two  parts  of  the  cocoon.    (Plate  I,  b.) 


THE  PUPA  STAGE. 

Within  forty-eight  hours  after  the  cocoon  is  started,  its  con- 
struction is  complete,  and  the  larva  has  thrown  off  its  skin  to 
assume  the  form  of  the  pupa,  a  less  active  stage  in  which  no  feed- 
ing is  done,  and  in  which  the  transformation  to  the  moth  form 
takes  place. 

The  pupa  is  less  than  one- fourth  of  an  inch  in  length,  not  more 
than  one-third  the  length  of  the  inner  cocoon,  is  brownish  in 
color  and  rather  blunt  at  the  ends.  The  rear  half  of  the  body  is 
quite  flexible,  and  when  disturbed,  the  pupa  wriggles  back  and 
forth  the  length  of  the  cocoon.  In  summer  the  pupal  stage  is 
passed  through  rapidly.  With  the  first  and  second  generations 
the  entire  period  from  the  spinning  of  the  cocoon  to  the  appear- 
ance of  the  moth  averaged  less  than  twelve  days,  while  with  the 
third  generation  the  process  was  retarded  by  cooler  weather,  and 
the  moths  emerging  late  in  November  had  spent  more  than  six 
weeks  in  the  cocoon.  As  time  for  emergence  approaches,  the  pupa 
becomes  darker.  When  the  moth  is  about  to  emerge,  the  pupa 
wriggles  its  way  through  the  cocoon,  and  forces  almost  its  entire 
body  out  of  one  end.    Then  the  skin  bursts,  and  the  moth  appears. 


256  CONNECTICUT  EXPERIMENT  STATION  BULLETIN   246. 

HABITS  OF  THE  MOTHS. 

The  moths  seem  to  be  inactive  at  night,  but  are  very  active  in 
the  daytime,  especially  if  the  weather  is  warm.  They  are  great 
lovers  of  flowers,  and  when  they  are  flying  in  great  numbers,  are 
to  be  found  in  abundance  on  flowers  of  all  kinds.  In  the  vicinity 
of  Wallingford,  the  moths  have  been  noted  on  the  flowers  of  wild 
carrot,  goldenrod,  tansy,  yarrow,  cultivated  zinnias,  calHopsis  and 
many  others.  After  the  flowers  have  been  killed  by  the  frost,  the 
moths  seem  to  pay  no  further  attention  to  them.  The  moths  be- 
came extremely  abundant  during  the  latter  part  of  September. 
Moths  alighting  on  window  screens  were  noted  everywhere,  and 
as  many  as  thirty-two  were  counted  on  one  screen  at  one  time. 

DISSEMINATION  OF  THE  MOTHS. 

The  most  rapid  dissemination  seems  to  occur  in  the  moth  stage. 
During  October  immense  numbers  of  moths  were  observed  at 
Amherst,  Mass.,  seemingly  more  than  could  have  emerged  nearby, 
judging  from  the  infestation  in  the  immediate  vicinity.  Presum- 
ably many  of  these  moths  had  come  from  the  more  heavily  in- 
fested areas  in  Connecticut  at  times  when  a  strong  wind  was  blow- 
ing from  the  south  or  southwest.  This  seems  the  simplest  way  of 
accounting  for  the  rapid  spread  of  the  species  across  the  States  of 
Connecticut  and  Massachusetts  within  a  period  of  not  more  than 
three  years. 

FOURTH    GENERATION. 

During  a  period  of  unusually  warm  weather  the  first  few  days 
in  October,  a  few  of  the  third  brood  moths  laid  eggs,  both  in  in- 
sectary  cages  and  in  the  field.  After  an  incubation  period  of  10 
to  12  days,  these  eggs  hatched,  but  sharp  freezes  the  19th  and  21st 
of  October  killed  nearly  all  the  apple  foliage,  cutting  off  the  food 
supply  before  many  of  these  larvae  had  passed  the  first  instar. 

HIBERNATION. 

The  stage  in  which  the  species  passes  the  winter  seems  to  be  in 
doubt.  Mention  is  made  in  English  entomological  literature  of  the 
collection  of  the  moths  from  roof  thatch  in  very  late  fall  and  in 
very  early  spring.  In  German  publications  the  statement  is  found 
that  probably  both  pupae  and  adults  winter  over.  In  Wallingford 
attempts  to  carry  both  stages  through  the  winter  of  1921-22  failed. 
In  1922,  the  emergence  from  pupae  of  the  third  generation  was 
very  nearly  complete,  although  the  last  moths  to  emerge  did  not 
leave  the  cocoons  until  late  November.  An  examination  of  158 
cocoons  collected  at  random  near  the  Wallingford  station  on 
November  24th  yielded  only  one  living  pupa,  while  examination  of 


APPLE   AND   THORN    SKELETONIZER.  257 

a  large  number  at  New  Haven  yielded  no  live  examples.  -Evidently 
the  greater  part,  if'  not  all,  of  the  insect^  will  pass  the  winter  of 
1922-23  as  adults.  Probably  the  moths  which  were  seen  in  such 
numbers  on  windows  and  screens  in  the  fall  were  in  search  of 
satisfactory  places  to  spend  the  winter.  Of  104  moths  which 
emerged  from  September  5th  to  15th,  and  which  were  kept  in 
glass  cages,  less  than  20  per  cent,  had  died  by  the  latter  part  of 
November.  Examination  of  these  February  21,  as  well  as  those 
in  other  cages,  showed  that  about  15  per  cent,  were  still  alive.  It 
seems  almost  certain,  therefore,  that  some  of  the  moths  will  sur- 
vive the  winter. 

Under  different  seasonal  and  weather  conditions,  the  last  brood 
of  larvae  might  complete  their  feeding  later  in  the  fall,  and  pupa- 
tion might  occur  so  late  that  many  individuals  would  pass  the  win- 
ter in  the  cocoons  and  emerge  in  the  early  spring.  In  November 
of  1922,  however,  moths  emerged  from  cocoons  spun  as  late  as 
October  8th. 

LIFE   HISTORY   DATA. 

Table  1  gives  in  condensed  form  the  information  secured  at  the 
Wallingford  station  on  the  seasonal  history  of  this  insect  during 
1922.  The  records  for  the  first  two  generations  are  incomplete, 
but  estimates  have  been  made  of  the  dates  when  egg-laying  and 
hatching  probably  occurred.  With  these  two  generations  the  in- 
formation regarding  cocooning,  pupation,  and  emergence  was 
secured  from  material  in  all  larval  stages  collected  in  the  field 
when  the  most  advanced  larvae  were  about  to  spin  cocoons.  Data 
for  the  third  and  fourth  generations  were  obtained  from  material 
reared  from  eggs  laid  in  the  insectary. 

The  periods  during  which  the  difiFerent  biological  events 
occurred  are  represented  graphically  in  Fig.  2.  As  a  guide  to 
efifective  application  of  control  measures,  the  periods  when  larvae 
of  the  successive  generations  were  present  on  the  trees  are  shown 
in  the  lower  part  of  the  graph.  The  dates  when  the  usual  spray 
applications  should  have  been  made  that  particular  season  are 
also  shown. 


258  CONNECTICUT  EXPERIMENT  STATION   BULLETIN   246. 


^pril 


Maij 


June 


Jxilij 


Aug. 


Sept. 


Oct. 


PI0V. 


Laying  or 


sggs 


Fl  R.ST 

Generation 


Hatching  of  eggs 

Cocooning  period. 

I 

Emergence  of  moths 


Eitimated 
Period} 


o 


Second 

&EnERATIOM 


Laying  cf.  eggs 

Hatching   of  eggs 

Cocooning  period 

Emecgeiue  of  moths 


Thiizd 

&EnEf^ATION 


Laying    of     eggs 

I  I 

hatching   ofi  eggs 

Cocooning     period 

Emergence    of   motti3 


Fbu/^TM       &EneiZATiorv 


Laying  of,  eggs 

tiatciiing  of   eggs . 


•         Dates    of    spray   applications 


Figure  3.     Chart  of  the  life  history  of  the  apple  and  thorn  skeletonizer. 
Stippled  areas  are  estimated  periods. 


APPLE   AND   THORN    SKELETONIZER. 


259 


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26o.        connecticut  experiment  station  bulletin  246. 

Natural  Enemies. 

A  number  of  natural  enemies  have  been  observed  preying  on  the 
skeletonizer.  An  encouraging  feature  of  the  work  of  parasites 
has  been  the  wide  variety  of  forms  which  seem  to  be  adapting 
themselves  to  this  new  host,  although  most  of  them  have  been 
reared  in  small  numbers.  One  Russian  publication  dealing  with 
this  insect  (abstracted  in  Rev.  Appl.  Ent.,  I,  p.  489)  states  that 
a  high  percentage  of  parasitism  occurred  in  the  region  under  dis- 
cussion. It  is  to  be  hoped  that  a  similar  condition  will  be  speedily 
reached  in  this  country,  although  as  yet  the  combined  eflforts  of  all 
enemies  have  not  been  sufficient  to  keep  pace  with  the  rapid  multi- 
plication of  the  host.  A  report  from  Fairfield  County  in  1922, 
however,  indicates  that  the  skeletonizer  infestation  has  been  some- 
what less  severe  than  in  the  preceding  year,  which  we  may  hope 
is  due  to  an  increase  of  natural  enemies. 

Mr.  Bromley  noted  a  number  of  chipping  sparrows  which  were 
apparently  feeding  on  the  skeletonizer  larvae.  He  also  observed 
a  spider  feeding  on  a  moth,  and  another  moth  which  had  been  cap- 
tured by  an  ambush  bug  of  the  family  Phymatidae.  An  immature 
Pentatomid,  probably  a  species  of  Podisus,  was  observed  sucking 
the  juices  from  a  small  larva. 

The  following  parasites  have  been  reared  in  Connecticut* : 

Habrobracon  gelechiae  (Ashmead).  Parasitic  on  or  in  the 
larva  which  collapses  before  becoming  full  grown.  Collected  at 
Bantam. 

Diodes  ohliteratus  (Cresson).  Oviposition  in  the  two-thirds  to 
nearly  full  grown  host  larva ;  emergence  from  the  host  cocoon. 
Reared  from  Wallingford  material,  and  has  also  been  reared  from 
the  skeletonizer  in  New  York  State. 

Sagaritis  sp.  Life  history  similar  to  that  of  Diodes.  Reared  at 
Wallingford. 

Exochus  propinquus  Cresson.  Oviposition  in  nearly  full  grown 
larva;  emergence  from  host  cocoon.    Wallingford. 

Epiurus  indagator  (Cresson).  Oviposition  in  full  grown  larva; 
emergence  from  host  cocoon.    Wallingford  and  Southington. 

Dibrachys  boucheanus  (Ratzeburg).  This  omnivorous  para- 
site oviposits  in  the  host  pupa  in  the  cocoon.    Wallingford. 

Exorista  pyste  Walker.  The  pearly  white  eggs  of  this  species 
are  placed  on  the  nearly  full  grown  host  larvae.  Cocooning  and 
pupation  occur  as  usual,  but  the  pupa  is  killed  by  the  parasite  mag- 
got from  which  the  fly  later  emerges.     New  Haven  and  Walling- 


*D.  boucheanus  determined  by  Mr.  S.  A.  Rohwer ;  other  Hymenopterous 
parasites  determined  by  Mr.  R.  A.  Cushman ;  all  Dipterous  parasites  de- 
termined by  Dr.  J.  M.  Aldrich. 


APPLE   AND   THORN    SKELETONIZER.  '  '261 

ford,  and  has  also  been  reported  from  New  York  State  as  para- 
sitizing the  skeletonizer. 

Phorocera  tortricis  Coquillett.  Life  history  similar  to  that  of 
Exorista  pyste.     Wallingford. 

Nemorilla  maculosa  Meigen.  A  single  individual  emerged  from 
a  host  pupa.  Probably  oviposition  or  larviposition  occurs  in  or  on 
host  larva.     Wallingford. 

The  following  parasites  have  been  recorded  from  Europe : 

Angitia  glabricola  Holmgren ;  Mesochorus  pectoralis  Ragonot ; 
Microgasfer  sp. ;  Phygadenon  sp. ;  Thryptocera  crassicornis 
Meigen. 

Control. 

A  review  of  the  feeding  habits  of  the  skeletonizer  larvae  will 
show  that  the  pest  should  be  easily  controlled  by  the  use  of  arsenate 
of  lead,  the  standard  poison  for  leaf-chewing  insects.  For  a  week 
or  more  after  hatching,  the  young  larvae  feed  on  the  under  sides 
of  the  leaves,  but  before  they  have  become  very  large,  and  before 
extensive  feeding  has  been  done,  they  migrate  to  the  upper  sur- 
faces, and  complete  their  feeding  there.  Often  one  leaf  will  be 
deserted  for  another  nearby.  If  the  lower  surfaces  of  the  leaves 
are  well  coated  with  poison  before  the  eggs  hatch,  the  newly 
hatched  larvae  should  be  easily  killed.  If  the  upper  sides  of  the 
leaves  are  thoroughly  covered,  the  larvae  on  migrating  there  from 
their  first  feeding  grounds  will  consume  much  of  this  poison. 

These  assumptions  were  confirmed  by  laboratory  experiments 
carried  on  at  the  Wallingford  station.  On  August  12th,  24  newly 
hatched  larvae  were  placed  on  each  of  two  apple  branches  sprayed 
with  powdered  arsenate  of  lead  at  the  rate  of  one  pound  in  50 
gallons  of  water,  special  care  having  been  taken  to  cover  the  under 
sides.  Twenty- four  newly  hatched  larvae  were  similarly  placed 
on  each  of  two  unsprayed  branches.  An  examination  of  the 
foliage  nine  days  later  showed  that  34  out  of  the  48  placed  on  the 
unsprayed  twigs  had  survived,  whereas  none  could  be  found  on 
the  sprayed.  With  third  and  fourth  instar  larvae,  nearly  one  hun- 
dred per  cent,  kill  was  obtained  with  arsenate  of  lead  at  the  rate 
of  one  pound  of  the  powdered  form  in  50  gallons  of  water.  Only 
one  larva  survived  the  treatment,  this  individual  spinning  its 
cocoon  four  days  after  being  placed  on  the  sprayed  foliage. 
Equal! V  good  control  was  obtained  with  the  use  of  only  half  this 
strength  of  the  poison.  From  these  experiments  it  is  evident  that 
a  thorough  application  of  arsenate  of  lead  at  the  usual  strength, 
and  even  at  a  lesser  strength,  will  kill  all  but  the  nearly  full  grown 
larvae,  which  apparently  may  not  consume  enough  poison  before 
cocooning  to  kill  them. 


:262  CONNECTICUT  EXPERIMENT  STATION   BULLETIN   246. 

It  is  next  necessary  to  consider  the  proper  time  for  the  applica- 
tions. The  periods  during  which  the  larvae  are  to  be  found  feed- 
ing on  the  foliage  are  shown  graphically  in  Fig.  3.  A  single  ap- 
plication early  in  the  feeding  period  of  each  generation  should  give 
satisfactory  control.  During  1922  these  points  were  reached  ap- 
proximately as  follows :  1st  generation,  about  May  15th,  during 
the  latter  part  of  the  blooming  period  of  the  apple;  2nd  genera- 
tion, about  July  4th,  about  seven  weeks  after  apple  blossom  time ; 
3rd  generation,  about  August  20th,  approximately  14  weeks  after 
apple  blooming. 

In  practice,  the  commercial  fruit  grower  will  get  fairly  good 
•control  of  the  skeletonizer  if  he  follows  the  usual  spray  schedule 
recommended  for  the  control  of  other  orchard  insects.  A  majority 
of  the  first  brood  of  skeletonizer  larvae  will  be  poisoned  by  the 
arsenate  of  lead  in  the  so-called  pink  and  calyx  applications,  and 
fairly  good  control  should  result  from  the  latter  application  alone. 
The  second  brood  should  be  well  controlled  by  the  first  apple  mag- 
got spray  early  in  July.  Where  this  application  is  unnecessary, 
enough  poison  will  probably  remain  from  the  spray  for  codling 
moth  control  (put  on  the  middle  of  June  or  three  or  four  weeks 
after  the  calyx  spray)  to  kill  at  least  the  early  part  of  the  second 
generation  of-  skeletonizer  larvae.  The  later  part  of  the  same 
larood  will  be  poisoned  by  the  second  brood  codling  moth  spray, 
applied  the  latter  part  of  July,  approximately  ten  weeks  after  the 
calyx  application.  Enough  of  this  last  mentioned  application  will 
probably  be  still  present  during  August,  when  the  third  brood  of 
skeletonizer  larvae  appears.  Fruit  growers  should  be  on  the  look- 
out for  the  third  brood  during  August,  and  if  an  infestation 
threatens,  due  to  a  migration  of  moths  into  the  orchard,  it  may  be 
worth  while  to  make  a  special  application  as  soon  as  larvae  are 
present  in  numbers.  In  1922,  this  occurred  soon  after  the  middle 
of  August.  This  probably  is  the  only  application  which  may  be 
needed  in  addition  to  those  included  in  the  regular  spray  schedule. 
Young  non-bearing  orchards  should  have  a  fair  amount  of 
arsenical  poison  on  the  foliage  during  the  early  part  of  the  feeding 
period  of  each  larval  brood ;  otherwise  partial  skeletonization  if 
not  complete  defoliation  may  occur,  and  growth  will  be  corres- 
pondingly retarded. 

In  an  exceptionally  warm  and  favorable  season,  or  in  regions 
further  south, ,  a  fourth  generation  might  become  of  importance, 
but  this  is  not, likely  to  occur  in  Connecticut.  In  1922  the  tempera- 
ture at  New  Haveni  for  May  was  approximately  60°  F. ;  June,  68" 


1  This  approximates  a  mean  temperature,  is  based  on  records  taken  at 
ei^^ht  o'clock  P.  M.,  and  was  computed  on  a  system  worked  out  by  F.  Z. 
Hartzell,  Technical  Bulletin  No.  68,  New  York  Agricultural  Experiment 
Station,  Geneva.  N.  Y.,  June,  1919. 


APPLE   AND   THORN    SKELETONIZER.  263 

F. ;  July,  69°  F. ;  August,  71°  F. ;  September,  68°  F. ;  and  October, 
62°  F. 

Summary. 

The  apple  and  thorn  skeletonizer,  an  insect  well  known  in 
Europe  for  over  one  and  one-half  centuries,  was  discovered  in 
the  lower  Hudson  Valley  in  1917,  and  in  southwestern  Connecti- 
cut in  1920.  Since  then  it  has  spread  up  the  Hudson  to  Albany, 
over  nearly  the  entire  State  of  Connecticut,  and  into  western 
Massachusetts.  Many  neglected  orchards,  small  home  orchards, 
and  roadside  trees  have  been  nearly  defoliated  by  this  insect  in 
many  parts  of  Connecticut, 

In  Connecticut  the  species  passed  through  three  generations 
during  the  season  of  1922,  larvae  of  the  first  generation  being 
present  on  the  trees  during  May  and  early  June ;  those  of  the 
second  from  late  June  to  early  August ;  and  those  of  the  third 
from  August  to  the  middle  of  October.  A  very  fractional  fourth 
generation  started  during  an  unusually  warm  period  in  October, 
but  a  freeze  ruined  the  food  supply  before  any  of  the  larvae  had 
passed  beyond  the  early  instars.  Hibernation  in  the  winter  of 
1922-23  will  occur  almost  entirely  in  the  adult  stage ;  under  cer- 
tain conditions  some  individuals  may  hibernate  in  the  pupal  stage. 

A  number  of  different  parasites  have  been  reared  from  the  larvae 
and  pupae  of  the  skeletonizer,  for  the  most  part  in  small  numbers. 
It  is  to  be  hoped  that  these  and  other  natural  enemies  will  increase 
in  numbers  and  effectiveness,  and  will  in  the  near  future  bring  this 
new  pest  within  more  reasonable  bounds. 

The  usual  spray  schedule  will  ordinarily  keep  the  skeletonizer 
under  control.  The  third  generation  will  probably  cause  the  most 
trouble  in  commercial  orchards.  In  case  this  brood  threatens 
serious  damage,  it  can  be  easily  controlled  by  an  additional  appli- 
cation of  arsenate  of  lead  at  the  rate  of  one  pound  of  the  dry  form 
in  50  gallons  of  water,  put  on  when  the  larvae  are  becoming  numer- 
ous, the  middle  to  the  latter  part  of  August. 


Bibliography. 
Clerck — 

1759— Ic._  Ins.  t.  10,  f.  9. 
Original  description. 
Bower,  B.  A. 

1890— /n  Ent.  Mon.  Mag.,  26,  p.  271. 

Moths  collected  in  thatch  in  fall  and  in  early  spring. 
Fernald,  C.  H. 

1900— /;j  Can.  Ent.,  32,  p.  236. 

Synonymy    cleared   up,    and   the    correct    scientific    name    of    the 
species  shown  to  be  Hemerophila  pariana  (Clerck). 


264  CONNECTICUT  EXPERIMENT  STATION   BULLETIN   246. 

Reh,  L. 

1913 — Handbuch    der    Pflanzenkrankheiten,    dritter    Band,    pp.    274-275. 
Brief  account  of  life  history,  food  plants,  and  parasites  in  Europe. 
Felt,  E.  P. 

1917— 7n  Journ.  Econ.  Ent.,  10,  p.  502. 

Report  of  first  discovery  in  the  United  States. 
Felt,  E.  P. 

1918— Cornell  Extension  Bulletin  No.  27. 
In  Rep't  Ont.  Ent.  Soc,  48,  p.  44. 
In  Rep't  N.  Y.  State  Entomologist,  ZZ,  p.  ZZ. 
Illustrated   account,   giving  habits,   descriptions,   partial   life   his- 
tory, and  bibliography. 
Britton,  W.  E. 

1921 — In  20th  Rep't  State  Entomologist  of  Connecticut  for  1920,  pp. 
190-193. 

Records  first  discovery  in  Connecticut.    General  account. 
Britton,  W.  E. 

1922 — In  21st  Rep't  State  Entomologist  of  Connecticut  for  1921,  pp. 
186-188. 

Rapid  spread  of  the  insect  over  most  of  Connecticut  recorded. 
Rearing  of  parasite,  Exorista  pyste,  Walker. 
Felt,  E.  P. 

1922— /n  The  Insect  Pest  Survey  Bulletin,  II,  p.  239. 

Record  of  spread  northward  in  Hudson  Valley  to  Albany. 
Fernald,  H.  T. 

1922— /n  The  Insect  Pest  Survey  Bulletin,  II,  p.  267. 
First  record  from  western  Massachusetts. 
Kuwayama,  S. 

1922 — In  Journal  of  the  Hokkaido  Agric.  Soc,  Sapporo,  Japan,  XXII, 
No.  254-255,  pp.  1-14.  (Reviewed  in  Rev.  Appl.  Ent.,  _X,  p.  487). 
Record  of  recent  discovery  in  Sapporo  and  Aomori,  in  northern 
Japan. 


PLATE  I. 


a.  Characteristic  injury  of  larvae  on  apple  leaves,  somewhat  reduced. 


b.     Cocoon  on  under  surface  of  apple  leaf,  twice  natural  size. 
APPLE  AND  THORN  SKELETONIZER. 


PLATE  II. 


a.  Larva,  enlarged  four  times. 


b.   Moth  resting,  enlarged 
three  and  one-half  times. 


c.  Pupae,  enlarged 
about  five  times. 


d.  Adults,  enlarged  four  times. 


APPLE  AND  THORN  SKELETONIZER. 


PLATE  III. 


a.  Cocoon  on  leaf,  showing  double-walled  construction,  somewhat  reduced. 


.\  -.=.  -i5fa^-i*^*Kis: 


b.  Eggs  on  under  surface  of  leaf,  enlarged  five  times. 


c.  Larva  on  leaf,  natural  size. 
APPLE  AND  THORN  SKELETONIZER. 


PLATE  IV. 


5388      7  2 


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Connecticut 

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